DESCRIPTION (Applicant's Description): Genomic imprinting results in parent-of-origin dependent monoallelic expression of certain genes in the offspring. T h e o retical arguments and limited experimental data suggest that a disproportionate number of imprinted genes may be involved in the control of fetal and placental growth. Low-resolution mapping and mechanistic models suggest that genomic imprinting may be regional, with particular chromosomal segments containing clusters of imprinted genes. These two features of imprinting could help to explain the involvement of imprinted chromosomal regions in the pathogenesis of certain human embryonal tumors. A major interest of the applicants' laboratory is to test the hypothesis that there is an extended imprinted domain on chromosome 11p15.5 and that there are multiple imprinted genes in this chromosomal region which contribute to normal growth control and embryonal tumorigenesis. The applicants have assembled a clone contig spanning 700 Kb of chromosome 11p15.5. This contig lies within the minimal region subject to loss of maternal alleles in Wilms' tumor (WT) and includes several known imprinted genes. Exon-trapping of this contig has uncovered 6 new genes, and gene-isolation efforts are ongoing. The first of these genes which they chose for analysis, IPL (imprinted in placenta and liver), encodes a major placental transcript. The predicted protein product of this gene shows sequence similarity to a lymphocyte transcript, TDAG51, which appears to be involved in rendering cells susceptible to apoptosis. They have found that the IPL gene is monoallelically expressed in human placenta, and this is likely to reflect parental imprinting. While IPL is not likely to be a WT gene, it may regulate growth of the normal placenta, and may thus also play a role in placental neoplasia. The current proposal is to investigate the biological role of the IPL gene and to isolate and characterize additional imprinted genes from this region of chromosome 11p15.5 which regulate growth of the fetus and placenta. In Aim 1 the applicants will isolate the mouse orthologue of the IPL gene, they will test the imprinting of murine Ip1 using interspecific mouse crosses and they will determine its intron/exon structure. In Aim 2 they will characterize the biological function of the mouse and human IPL gene by in situ hybridization studies, by eukaryotic expression systems, and by construction of germline-deletion mice. In Aim 3 they will extend their analysis of IPL to neoplastic human placental tissues. In Aim 4 they will isolate additional imprinted genes from their chromosome 11p15.5 clone contig and study them in terms of their effects on normal fetal and placental growth by approaches similar to those described for the IPL gene.